1. Field of the Invention
The present invention relates to an error signal detection apparatus and method for an optical recording/reproducing system, and more particularly, to an error signal detection apparatus and method for an optical recording/reproducing system in which a tilt error signal between an objective lens and a recording medium can be detected using a main beam focused to record/reproduce an information signal on the recording medium.
2. Description of the Related Art
Optical pickups record an information signal on or reproduce an information signal from a recording medium, such as an optical disc seated on a turntable and rotating, while scanning the recording medium in the radial direction. However, if the rotating optical disc is tilted with respect to the optical axis, due to bending of the optical disc itself or error in loading the disc, degradation of a recording/reproduction signal can result.
When an optical pickup adopts a light source which emits a shorter wavelength of light, and an objective lens having a high numerical aperture (NA), for the purpose of increasing recording density, coma aberration caused by tilting of the optical disc increases, thereby further degrading the recording/reproduction signal. This is because optical aberration is proportional to λ/(NA)3.
In an optical recording/reproducing system required for high-density recording and reproduction with a medium, such as a digital versatile disc (DVD) and/or future generation DVD (so-called high definition (HD)-DVD), there is a need for a tilt error signal detection apparatus capable of preventing degradation of the recording/reproduction signal by detecting the degree of tilting between the objective lens and the disc and correcting for the tilting of the disc.
On the other hand, as shown in FIG. 1, light reflected by a disc 10, after having been focused on the disc 10 for recording/reproduction, is diffracted into a 0th order diffracted beam and ±1st order diffracted beams by record marks such as pits (P) formed on the tracks of the disc 10. The reflected light passes through objective lens 7. Thus, a photodetector 9 receives the 0th order diffracted beam and ±1st order diffracted beams, which overlap each other in the radial direction. FIG. 1 illustrates light reflected and diffracted in the radial direction from a high-density disc having narrow tracks, e.g., a ROM type disc. This shows the case where spots formed on the photodetector 9 by the ±1st order diffracted beams are separated from each other, and each of the spots overlaps the spot formed by 0th order diffracted beam.